Transmission image capturing system and transmission image capturing method

ABSTRACT

The present invention proposes a technique capable of accurately grasping position and angle of a radiation generator at the time of image capturing. At the time of obtaining a plurality of transmission images by detecting radiation emitted from a emitting generator and passing through a specimen via a predetermined member (for example, a diaphragm) by a detector for a plurality of times while changing a relative position relation and a relative angle relation of the emitting generator to the detector, an outer-edge shape of a radiation area irradiated with the radiation on a detection surface of the detector from the emitting generator is recognized. On the basis of the outer-edge shape of the radiation area and an inner-edge shape of a predetermined member, the relative position relation and the relative angle relation of the emitting generator to the detector are obtained.

This application is based on application No. 2007-178396 filed in Japan,the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission image capturingtechnique.

2. Description of the Background Art

In medical fields, transmission images of a human body are captured byusing X ray or the like. By reading the transmission images, diagnosisis conducted.

An X-ray diagnosing apparatus for so-called tomosynthesis is proposed,capable of observing a slice plane of a specimen at an arbitrary depthby synthesizing (reconstructing) a plurality of pieces of image dataobtained by irradiating the specimen with X ray in different directionsby image capturing using X ray.

At the time of capturing a plurality of projection images to generate animage of a slice plane, the position and angle of a scan system such asa part that emits radiation (for example, an X-ray tube) tend to bedeviated from settings. Due to the deviation, so-called artifact such asdistortion occurs in an image of a slice plane reconstructed. It isconsequently very important to accurately grasp the position and angleof a part for generating radiation (radiation generating part) at thetime of capturing a projection image.

To address such a problem, a technique of disposing a chart forcalibration made of two microspheres, performing image capturing, andcalibrating a scan system on the basis of the position of the chart forcalibration in a projection image, thereby grasping the position andangle of a radiation generator more accurately and performing moreaccurate reconstruction has been proposed (for example, JapaneseUnexamined Patent Application Publication No. 2003-61944).

However, in the technique proposed in Japanese Unexamined PatentApplication Publication No. 2003-61944, calibration is performed inadvance using the chart for calibration before image capturing. In thecase where a different deviation occurs in the scan system at the timeof image capturing, the position and angle of a radiation generator atthe time of image capturing cannot be accurately grasped, and it isdifficult to perform accurate reconstruction.

SUMMARY OF THE INVENTION

The present invention is directed to a transmission image capturingsystem.

According to the invention, the transmission image capturing systemincludes: a generator for generating radiation; a predetermined memberfor specifying a radiation path of the radiation by its inner-edgeshape; a detector for detecting radiation emitted from the generator andpassing through a specimen via the predetermined member; an obtainingunit for obtaining a plurality of transmission images of the specimen bydetecting the radiation for a plurality of times by the detector whilechanging a relative position relation and a relative angle relation ofthe generator to the detector; and a computing unit for obtaining therelative position and angle relations on the basis of an outer-edgeshape of a radiation area which is irradiated with the radiation emittedfrom the generator to a detection surface of the detector and theinner-edge shape of the predetermined member.

With the configuration, the position and the angle of the radiationgenerator at the time of image capturing can be grasped accurately.

The present invention is also directed to a transmission image capturingmethod of obtaining a plurality of transmission images by detectingradiation emitted from a generator and passing through a specimen via apredetermined member for a plurality of times by a detector whilechanging a relative position relation and a relative angle relation ofthe generator to the detector.

Therefore, an object of the present invention is to provide a techniquecapable of accurately grasping position and angle of a radiationgenerator at the time of image capturing.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a schematic configuration of an imagecapturing system of a first preferred embodiment;

FIGS. 2A and 2B are diagrams for explaining the configuration of aemitting generator in the first preferred embodiment;

FIG. 3 is a diagram illustrating the functional configuration of acontrol unit in the first preferred embodiment;

FIG. 4 is a diagram for explaining the principle of the method ofrecognizing an outer-edge shape of a radiation area;

FIG. 5 is a diagram for explaining the principle of the method ofrecognizing the outer-edge shape of the radiation area;

FIGS. 6A and 6B are diagrams for explaining the principle of derivingthe position relation and the angle relation between the emittinggenerator and a detector;

FIGS. 7A and 7B are diagrams for explaining the principle of derivingthe position relation and the angle relation between the emittinggenerator and the detector;

FIG. 8 is a diagram for explaining the principle of deriving theposition relation and the angle relation between the emitting generatorand the detector;

FIG. 9 is a diagram for explaining the principle of deriving theposition relation and the angle relation between the emitting generatorand the detector;

FIG. 10 is a flowchart showing an image capturing operation flow of thefirst preferred embodiment;

FIG. 11 is a schematic diagram showing the principle of tomosynthesis;

FIGS. 12A and 12B are schematic diagrams showing the principle oftomosynthesis;

FIG. 13 is a diagram showing a schematic configuration of an imagecapturing system of a second preferred embodiment;

FIG. 14 is a diagram for explaining the configuration of a emittinggenerator in the second preferred embodiment;

FIG. 15 is a diagram for explaining the principle of a method ofrecognizing the outer-edge shape of the radiation area;

FIG. 16 is a diagram illustrating the functional configuration of acontrol unit in the second preferred embodiment; and

FIG. 17 is a flowchart showing an image capturing operation flow in thesecond preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the drawings.

First Preferred Embodiment Schematic Configuration of Image CapturingSystem

FIG. 1 is a diagram showing a schematic configuration of an imagecapturing system 1 of a first preferred embodiment of the presentinvention. The image capturing system 1 detects a distribution ofradiation passing through a specimen 120 by using radiation (typically,X ray), and obtains a distribution of pixel values (transmission image),so that various information processes using the transmission image canbe performed. That is, the image capturing system 1 functions as asystem for capturing a transmission image (transmission image capturingsystem).

The image capturing system 1 includes an image capturing apparatus 100and an image capture control processing apparatus 200. It is assumedthat the specimen 120 as an object to image capturing is the body of aperson to take a test. An oval in the diagram schematically expressesthe body of the specimen.

The image capturing apparatus 100 has, mainly, a emitting generator 101,a guide 102, a mounting part 104, a coupling part 105, and a detector108.

The emitting generator 101 generates and emits radiation as a kind ofelectromagnetic waves. It is assumed here that the emitting generator101 generates and emits X rays. In FIG. 1 and subsequent diagrams,alternate long and short dash lines are drawn at the outer edges of thepath of emission of radiation.

FIGS. 2A and 2B are diagrams illustrating the configuration of theemitting generator 101. In FIGS. 2A and 2B and subsequent diagrams, toclarify the azimuth relation, three axes of X, Y, and Z which crossorthogonal to each other are properly shown.

FIG. 2A is a cross section diagram schematically showing theconfiguration of the emitting generator 101. The emitting generator 101is constructed by, for example, an X-ray tube and has a generating unit101 a and a diaphragm 101 c. In FIG. 2A, a radiation passage area isshaded.

The generating unit 101 a is a part for generating radiation, and thediaphragm 101 c is provided for the generating unit 101 a and functionsas a predetermined member that specifies the path of radiation(radiation path) emitted from the generating unit 101 a toward thespecimen 120, that is, the shape of the radiation path. By disposing thegenerating unit 101 a and the diaphragm 101 c, the emitting generator101 forms a focal point Fp of radiation (for example, focal point of anX-ray tube).

As shown in FIG. 2B, the diaphragm 101 c (a hatched portion in thediagram) has, for example, an opening 101 h of a square shape whoselength of one side has a predetermined value, that is, an inner-edgeshape. The distance from the focal point Fp to the opening 101 h,specifically, the distance from the focal point Fp to the center pointof the opening 101 h is set to be a predetermined distance.

By the shape of the opening 101 h, the outer edges of the radiation pathof the radiation form a square shape. Further, the size of the square asthe outer-edge shape of the radiation path increases in proportion todistance from the generating unit 101 a.

Referring again to FIG. 1, the explanation will be continued.

The guide 102 extends almost an arc shape and can change the positionand posture of the emitting generator 101. Concretely, the emittinggenerator 101 is movably coupled to the guide 102 in the extendingdirection and moves along the extending direction on the guide 102according to an image capture control processing apparatus 200.

The mounting unit 104 is a part on which the specimen 120 is left atrest. The mounting unit 104 is disposed so as to satisfy a predeterminedrelative disposing condition with respect to the emitting generator 101coupled to the guide 102 via the coupling unit 105. The specimen 120 ismounted within a radiation range of an X-ray emitted from the emittinggenerator 101. More specifically, the mounting unit 104 is fixed in apredetermined position on the side where the focal point of thearc-shaped part specified by the guide 102 is located.

The mounting unit 104 is made of a material substantially transmittingan X-ray by having small absorption of an X-ray, and X-ray attenuationcoefficient (absorption coefficient) is known. In a state where thespecimen 102 is left at rest on the mounting unit 104, the emittinggenerator 101 emits an X-ray while being properly moved along the guide102, thereby irradiating the specimen 120 with the X-ray from desireddirections.

The detector 108 detects the radiation (X-ray in this case) emitted fromthe emitting generator 101 and passed through the specimen 120 mountedon the mounting unit 104 and through the mounting unit 104. The detector108 detects, for example, both of the X ray passed through the specimen120 and the X-ray passed through the space around the specimen 120.

A surface on the side of emitting generator 101, of the detector 108,that is, an X-ray detecting surface (detection surface) 108 s has, forexample, a rectangular outer shape and has an almost flat surface inwhich a number of sensors for detecting X rays are arrangedtwo-dimensionally (for example, in a lattice shape). Therefore,radiation passed through the specimen 120 and the mounting unit 104 inthe radiation emitted from the emitting generator 101 is detected by thedetector 108, and a distribution of detection values of the radiation(in this case, a two-dimensional distribution having the lattice shape)is obtained.

The emitting generator 101, the guide 102, the mounting unit 104, andthe detector 108 satisfy positional relations described below.Specifically, since the radiation range of the X ray emitted from theemitting generator 101 covers a wide range of the mounting unit 104,even when the emitting generator 101 moves to any of positions on theguide 102, the X ray emitted from any of the positions on the guide 102is detected by the detector 108.

In FIG. 1, the guide 102 is formed almost in an arc shape, and theemitting generator 101 emits X ray toward the center point of the arc.The invention is not limited thereto. For example, the guide 102 may beextended almost linearly and the emitting generator 101 emits X ray in adirection almost perpendicular to the extending direction of the guide102 even when the emitting generator 101 moves to any position on theguide 102. In any of the cases, radiation is sequentially emitted in aplurality of directions to a predetermined side (upper side in FIG. 1)of the specimen 120, and a distribution of detection values of theradiation (hereinafter, also called “radiation detection valuedistribution”) is obtained.

On the other hand, the image capture control processing apparatus 200has a configuration similar to that of a general personal computer andincludes, mainly, a control unit 210, a display unit 220, an operatingunit 230, and a storing unit 240.

The control unit 210 has a CPU 210 a, a RAM 210 b, and a ROM 210 c, andcontrols the operations of the image capturing system 1 in a centralizedmanner. The control unit 210 realizes various functions and operationsby reading a program PG stored in the storing unit 240 and executing theprogram PG.

The display unit 220 is constructed by, for example, a liquid crystaldisplay and the like. Under control of the control unit 210, variousimages are visibly output. For example, a transmission image obtained byimage capturing of the image capturing apparatus 100 or the like isvisibly output.

More specifically, a planar image (plane image) and a stereoscopic imageviewed from a specific direction are visibly output. Concretely, notonly a plane image expressed by data of a transmission image(transmission image data) stored in the RAM 210 b and the like but alsoa stereoscopic image expressed by stereoscopic image data generated byan image generating unit 216 (to be described later), other variousimage information, numerical information, and character information aredisplayed. Display of a stereoscopic image viewed from a specificdirection as a two-dimensional image will be called “display of astereoscopic image” hereinafter.

The operating unit 230 includes a keyboard and a mouse, accepts variousinputs of the user, and transmits signals according to the inputs to thecontrol unit 210.

The storing unit 240 includes a hard disk and the like, and stores, forexample, the program PG for controlling various operations of the imagecapturing system 1, various data, and the like.

Functional Configuration in Control Unit

FIG. 3 is a diagram illustrating the functional configuration realizedwhen the program PG is executed by the control unit 210.

As shown in FIG. 3, the control unit 210 has, as functions, an imagecapturing control unit 211, a detection value obtaining unit 212, avalue converting unit 213, a radiation area recognizing unit 214, aposition/angle computing unit 215, and the image generating unit 216.

The image capturing control unit 211 controls operation of the imagecapturing apparatus 100. For example, the image capturing control unit211 controls the position of the emitting generator 101 on the guide102, thereby controlling the positional relation of the mounting unit104, that is, the specimen 120 to the emitting generator 101 and theguide 102. By this, the spatial relation between the emitting generator101 and the mounting unit 104 varies relatively. At this time, thedistance between the emitting generator 101 and the detector 108 and theangle relation between the emitting generator 101 and the detector 108are properly changed.

The “angle relation” includes the relation of the angle formed by thecenter line of radiation emitted from the emitting generator 101, thatis, the radiation travel direction and the surface (detection surface)108 s in which a number of sensors are arranged in the detector 108.

The detection value obtaining unit 212 accepts and obtains adistribution of detection values of radiation detected by the detector108. In the embodiment, a distribution of detection values detected bythe sensors disposed two-dimensionally in the detection surface 108 s,that is, a two-dimensional detection value distribution (two-dimensionaldistribution of the detection values) is obtained. The distribution ofdetection values obtained by the detection value obtaining unit 212 istemporarily stored in the RAM 210 b or the storing unit 240.

The value converting unit 213 converts the distribution of the detectionvalues obtained by the detection value obtaining unit 212 to adistribution of pixel values corresponding to a visible image(hereinafter, also called “pixel value distribution”), that is, imagedata. For example, a relatively large X-ray detection value is convertedto a pixel value of low luminance (low tone), and a relatively smallX-ray detection value is converted to a pixel value of high luminance(high tone). Image data (transmission image data, also called“transmission image”) is a two-dimensional distribution of pixel valuesand temporarily stored in the RAM 210 b or the storing unit 240.

By detecting radiation for a plurality of times by the detector 108while changing the relative position and angle relations of the emittinggenerator 101 to the detector 108 by the image capturing control unit211, a plurality of transmission images of the specimen 120 are obtainedby the value converting unit 213.

The radiation area recognizing unit 214 recognizes the shape of an areairradiated with radiation (hereinafter also called “radiation area” or“radiation field”) on the detection surface 108 s from the emittinggenerator 101, concretely, the shape of the outer edges (hereinafter,also called “outer-edge shape”) of the radiation area. A method ofrecognizing the outer-edge shape of the radiation area will be describedlater.

The position/angle computing unit 215 obtains the relative positionrelation and the relative angle relation between the emitting generator101 and the detector 108 by computation on the basis of the outer-edgeshape of the radiation area recognized by the radiation area recognizingunit 215 and the inner-edge shape of the diaphragm 101 c. A method ofcomputing the relative position relation and the relative angle relationwill be described later.

The image generating unit 216 generates various images (for example, animage of a slice plane) by using the transmission images obtained by thevalue converting unit 213.

For example, when a distribution of a plurality of pixel values, thatis, a plurality of transmission images are obtained while changing theposition of the emitting generator 101 along the guide 102, the imagegenerating unit 216 generates data of an image showing a slice plane(slice plane image) of the specimen 120 on the basis of the plurality oftransmission images and the relative position relation and the relativeangle relation of the emitting generator 101 to the detector 108 whenthe radiation of each of the transmission images is detected. The imagegenerating unit 216 also generates data of a stereoscopic image of thespecimen 120 having a three-dimensional structure on the basis of thedata of the slice plane image.

Concretely, for example, the image generating unit 216 generates data ofthe slice plane image while temporarily storing the data of thetransmission image into the RAM 210 b in cooperation with the RAM 210 bfor temporarily storing data. Further, the image generating unit 216generates data of the stereoscopic image while temporarily storing thedata of the slice plane image into the RAM 210 b. A method of generatingthe data of the slice plane image will be described later.

Method of Recognizing Outer-Edge Shape of Radiation Area

FIGS. 4 and 5 are diagrams for explaining the principle of the method ofrecognizing the outer-edge shape of the radiation area in the radiationarea recognizing unit 214.

FIG. 4 is a diagram paying attention to the emitting generator 101, thedetector 108, and the specimen 120 at the time of imaging the specimen120. In FIG. 4, the focal point Fp of the emitting generator 101 isshown by a filled circle, the outer edges of radiation emitted from theemitting generator 101 to the specimen 120 are shown by alternate longand short dash lines, and center line (center axis) Lc of the radiationemitted from the emitting generator 101 to the specimen 120 is shown bya broken line. It is assumed that each of the outer edges of theradiation emitted from the emitting generator 101 makes a predeterminedangle α to the center axis Lc.

In FIG. 4, the direction of emitting radiation from the emittinggenerator 101 to the specimen 120, that is, the travel direction ofradiation is inclined with respect to the normal line to the detectionsurface 108 s. Image capturing performed by irradiating the detectionsurface 108 s with radiation emitted obliquely will be also called“oblique image capturing”.

FIG. 5 is a diagram illustrating a transmission image G obtained at thetime of oblique image capturing as shown in FIG. 4. In the transmissionimage G, a pattern (trapezoidal image area which is shaded in thediagram) PA of the radiation emitted from the emitting generator 101 tothe detection surface 108 s appears. The pattern PA corresponds to thearea irradiated with the radiation from the emitting generator 101(radiation area) in the detection surface 108 s.

In FIG. 5, the outer edges of the pattern PA form a trapezoidal shape.However, the invention is not limited thereto. For example, at the timeof image capturing (facing-position image capturing) in which radiationis emitted from the emitting generator 101 in a state where theirradiation direction of the radiation from the emitting generator 101toward the specimen 120 is almost perpendicular to the detection surface108 s and the detector 108 detects the radiation, thereby obtaining adistribution of detection values, the outer shape of the pattern PA is asquare shape similar to the shape of the opening 101 h.

For example, the radiation area recognizing unit 214 recognizes thepattern PA of the radiation from the transmission image G obtained bythe value converter 213 and the outer-edge shape of the pattern PA,thereby recognizing the outer-edge shape of the radiation area of theradiation from the emitting generator 101 to the detection surface 108s. Concretely, the radiation area recognizing unit 214 recognizes thelength of the upper base, the length of the lower base, and the heightof the trapezoid as the outer-edge shape of the radiation area from thesize of the detection surface 108 s, the size of the projection image G,and the size of the pattern PA. That is, in the specification, the words“the outer-edge shape of the radiation area” are used for meaningincluding the size of the outer-edge shape, and the words “theinner-edge shape” are used for meaning including the size of theinner-edge shape.

Although the outer-edge shape of the radiation area is recognized fromthe transmission image G obtained by the value converting unit 213 inthe embodiment, the invention is not limited thereto. For example, theouter-edge shape of the radiation area may be recognized from adistribution of detection values obtained by the detection valueobtaining unit 212.

Principle of Deriving Position Relation and Angle Relation

FIGS. 6A and 6B to FIG. 9 are diagrams for explaining the principle ofderiving the relative position relation and the relative angle relationbetween the emitting generator 101 and the detector 108 in theposition/angle computing unit 215.

FIG. 6A is a sectional schematic view of the path of radiation seen froma side paying attention to the position relation between the emittinggenerator 101 and the detector 108. FIG. 6B is a diagram showing theouter-edge shape of the radiation area in the state of FIG. 6A.

The position/angle computing unit 215 computes the length of aperpendicular from the focal point Fp of the emitting generator 101 tothe detection surface 108 s, that is, distance “h” between the focalpoint Fp and the detection surface 108 s, and angle θ formed by thecenter line Lc of the radiation emitted from the emitting generator 101and a perpendicular from the focal point Fp to the detection surface 108s.

FIG. 7A is a diagram paying attention to the radiation path shown inFIG. 6A. FIG. 7B is a diagram paying attention to the outer-edge shapeof the radiation area shown in FIG. 6B.

As shown in FIGS. 7A and 7B, the distance from the focal point Fp to theopening 101 h is expressed as “d”, the distance from the focal point Fpto the center point of the upper base of the trapezoid as the outeredges of the radiation area is expressed as x1, the distance from thefocal point Fp to the center point of the lower base of the trapezoid asthe outer edges of the radiation area is expressed as x2, the length ofthe upper base of the trapezoid as the outer edges of the radiation areais expressed as “m”, the length of the lower base is expressed as “n”,and the height is expressed as “l”. The length of one side of theopening 101 h is set as a predetermined value “a”. Further, a squaresurface (virtual surface) Sf using the upper base of the trapezoid asthe outer edges of the radiation area as one side and perpendicular tothe center line Lc of the path of radiation is virtually set, and theangle formed between the detection surface 108 s and the virtual surfaceSf is expressed as φ.

Since the angle φ is the same as the angle θ, when the angle φ isobtained, the angle θ is obtained.

A method of calculating the angle φ (that is, the angle θ) and thedistance “h” will be described concretely below.

The predetermined value “a” and the distance “d” are known in designingof the emitting generator 101. The length “m” of the upper base, thelength “n” of the lower base, and the height “l” of the trapezoid as theouter-edge shape of the radiation area are recognized by the radiationarea recognizing unit 214. The distance from the center point of oneside on the lower base side of the trapezoid as the radiation area inthe vertical surface Sf to the center point of the lower base of thetrapezoid as the radiation area is calculated by “x2−x1”.

Since the regular square pyramid using the focal point Fp as an apex andusing the opening 101 h as a bottom face and the regular square pyramidusing the focal point Fp as an apex and using the virtual surface Sf asa bottom surface are similar figures, the distance x1 is obtained by thefollowing equation (1).

$\begin{matrix}{{x\; 1} = {{\frac{m}{a}\sqrt{( \frac{a}{2} )^{2} + d^{2}}} = {\frac{m}{a} \cdot {L( {{wherein},{L = \sqrt{( \frac{a}{2} )^{2} + d^{2}}}} )}}}} & ( {{Equation}\mspace{20mu} 1} )\end{matrix}$

FIG. 8 is a perspective view of the path of radiation. As shown in FIG.8, an isosceles triangle using the focal point Fp as an apex and theupper base of the trapezoid as the base, and an isosceles triangle usingthe focal point Fp as an apex and the lower base of the trapezoid as thebase are similar figures, and the ratio of the sizes is m:n.

Since the relation of x1:x2=m:n is satisfied, the distance x2 isobtained by the following equation (2).

$\begin{matrix}{{x\; 2} = {{x\;{1 \cdot \frac{n}{m}}} = {\frac{n}{a} \cdot {L( {{wherein},{L = \sqrt{( \frac{a}{2} )^{2} + d^{2}}}} )}}}} & ( {{Equation}\mspace{20mu} 2} )\end{matrix}$

Therefore, the lengths (l, m, and x2−x1) of the three sides of atriangle Tr drawn by the thick lines in FIG. 7A are obtained. From thelengths of the three sides forming the triangle Tr, the three internalangles of the triangle Tr are unconditionally obtained. That is, theangle φ (that is, the angle θ) is obtained.

FIG. 9 is a diagram for explaining concrete calculation of the distance“h”. In FIG. 9, a shape similar to that of FIG. 7A is drawn, and thetriangle Tr drawn by the thick lines in FIG. 7A is similarly drawn bythick lines.

As described above, when the lengths (l, m, and x2−x1) of the threesides of the triangle Tr are obtained, the internal angle ρ of the upperbase side of the trapezoid as the radiation area, as one of the internalangles of the triangle Tr, is also unconditionally obtained.

The distance “h” is obtained by the following equation (3).h=x2·sin ρ  (Equation 3)

When the distance “h” and the angle θ are obtained as described above,the relative position and angle relations between the emitting generator101 and the detector 108 are obtained unconditionally. For example, theposition (x, y, z) of the emitting generator 101 using a predeterminedpoint (for example, center point) of the detection surface 108 s as anoriginal point is obtained.

Image Capturing Operation Flow

FIG. 10 is a flowchart showing an image capturing operation flow ofcontinuously capturing transmission images of a plurality of frameswhile changing the radiation angle of X ray from the emitting generator101 to the specimen 120 in multiple stages in the image capturing system1. The operation flow is realized under control of, mainly, the imagecapturing control unit 211 when the control unit 210 executes theprogram PG. The operation flow starts when the specimen 120 is mountedon the mounting unit 104 and a predetermined input is entered from theoperating unit 230.

First, in step S1, by the control of the image capturing control unit211, the emitting generator 101 is set in an initial position.

The initial position of the emitting generator 101 on the guide 102 ispreset. It is assumed here that the initial position is set so that theirradiation angle of X ray from the emitting generator 101 to thespecimen 120 is the smallest. Concretely, the emitting generator 101 isdisposed, for example, at one end in the extending direction of theguide 102 (the right end in FIG. 1).

In step S2, by the control of the image capturing control unit 211,image capturing process is performed. The image capturing process isperformed here by emitting radiation from the emitting generator 101 tothe specimen 120 and detecting the radiation by the detector 108.

In step S3, on the basis of detection values of the radiation obtainedby the sensors in the detector 108 in step S2, the detection valueobtaining unit 212 obtains a two-dimensional distribution of thedetection values.

In step S4, the value converting unit 213 converts the two-dimensionaldistribution of the detection values obtained in step S3 to atwo-dimensional distribution of pixel values, thereby generating atransmission image.

In step S5, from the transmission image obtained in step S4, theradiation area recognizing unit 214 recognizes the outer-edge shape(concretely, the size) of the radiation area irradiated with theradiation in the detection surface 108 s. For example, the pattern PAcorresponding to the radiation area is recognized from the transmissionimage G as shown in FIG. 5, and the shape and size of the outer edgesare recognized.

In step S6, on the basis of the outer-edge shape of the radiation arearecognized in step S5 and the inner-edge shape of the diaphragm 101 c,the position/angle computing unit 215 calculates the relative positionrelation and the relative angle relation between the emitting generator101 and the detector 108. For example, by a method as described withreference to FIGS. 6A to 9, the distance “h” and the angle θ arecalculated, and the relative position and angle relations between theemitting generator 101 and the detector 108 are unconditionallycalculated from the distance “h” and the angle θ.

In step S7, whether the image capturing is finished or not isdetermined. For example, when a predetermined parameter reaches apredetermined value, it is determined to finish the image capturing.

Concretely, until the predetermined parameter reaches the predeterminedvalue, the emitting generator 101 is moved along the guide 102 in stepS8, and the program returns to step S2. On the other hand, when thepredetermined parameter reaches the predetermined value, the operationflow is finished.

At this time, a predetermined number of transmission images aresequentially obtained, and the relative position relation and therelative angle relation between the emitting generator 101 and thedetector 108 in each of image capturing processes corresponding to thetransmission images are calculated. Information indicative of therelative position relation and the relative angle relation between theemitting generator 101 and the detector 108 is associated with thetransmission image data and stored in the RAM 210 b or the storing unit240.

The predetermined parameters are the number of image capturing times,the travel distance of the emitting generator 101, the travel angle ofthe emitting generator 101, and the like. For example, until the numberof image capturing times reaches a predetermined number (for example,19), the processes in steps S2 to S8 are repeated. After the number ofimage capturing times reaches the predetermined number (for example,19), the operation flow is finished.

In step S8, by the control of the image capturing control unit 211, theemitting generator 101 is moved along the guide 102. The position of theemitting generator 101 on the guide 102 is changed from the position inthe image capturing process of last time to the next position. Forexample, in the case where the travel range along the extendingdirection of the guide 102 is divided in 18 parts and the emittinggenerator 101 moves in multiple stages, in step S8, the emittinggenerator 101 travels in the distance of 1/18 of the travel range.

Principle of Generation of Slice Plane Image Data

As described above, in the case where the position of the emittinggenerator 101 is varied along the guide 102 and a plurality oftransmission images are obtained sequentially, for example, by the imagegenerating unit 216, data of slice plane images (slice plane image data)of the specimen 120 is properly generated.

The principle of generating the slice plane image data, that is, theprinciple of tomosynthesis in the image generating unit 216 will bedescribed.

FIGS. 11 and 12 are schematic diagrams showing the principle oftomosynthesis.

In the tomosynthesis, radiation, concretely, X ray passing through thespecimen 120 is emitted at different angles on the side of one directionof the specimen 120 to the specimen 120 and data of a plurality oftransmission images is obtained and synthesized, thereby obtaining animage of a slice plane. The case where a star-shaped element 121 and around-shaped element 122 schematically showing internal structures(concretely, a human organ, a lesioned part, and the like) of thespecimen 120 are arranged in the direction perpendicular to thedetection surface 108 s as shown in FIG. 11 will be described as anexample.

As shown in FIG. 11, by emitting radiation to the specimen 120 atdifferent angles, data of a plurality of transmission images isobtained. In transmission images 41, 42, and 43 expressed by the data ofthe plurality of transmission images obtained in such a manner, thepositions of images of the elements vary according to the distance(height) from the detection surface 108 s. While utilizing thephenomenon, arbitrary slice plane image data is generated by using aknown method of synthesizing a plurality of images. One of the knownmethods of synthesizing a plurality of images in tomosynthesis isshift-and-add algorithm.

In shift-and-add algorithm, on the basis of the plurality oftransmission images 41 to 43 and the positions (x, y, z) and angles ofthe emitting generator 101 on detection of radiations corresponding tothe transmission images 41 to 43 (that is, in the image capturingprocess), a process of sequentially adding the transmission images whileshifting the relative positions of the transmission images 41 to 43 isperformed.

For example, as shown in FIG. 12A, an image 51 in which the star-shapedelement 121 which is vague in the transmission images 41 to 43 isemphasized is obtained. As shown in FIG. 12B, an image 52 in which theround-shaped element 122 which is vague in the transmission images 41 to43 is emphasized is obtained. The image 51 is a slice plane imageobtained by emphasizing a cross section at height where the star-shapedelement 121 exists in the internal structure of the specimen 120. Theimage 52 is a slice plane image obtained by emphasizing a cross sectionat height where the round-shaped element 122 exists in the internalstructure of the specimen 120.

The example of generating the images 51 and 52 by synthesizing the threetransmission images 41 to 43 by addition has been described to simplifythe explanation. In practice, a number of transmission images areobtained and synthesized.

As described above, in the image capturing system 1 of the firstpreferred embodiment of the invention, on the basis of the outer-edgeshape of the radiation area irradiated with radiation on the detectionsurface 108 s and the inner-edge shape of a predetermined member (forexample, the diaphragm 101 c) specifying the path of radiation, therelative position relation and the relative angle relation of theemitting generator 101 to the detector 108 are obtained. That is, at thetime of actual image capturing, the relative position and anglerelations of the emitting generator 101 with respect to the detector 108are obtained. Consequently, the position and angle of the emittinggenerator 101 at the time of image capturing can be grasped accurately.

On the basis of the outer-edge shape of the radiation area irradiatedwith ration on the detection surface 108 s and the inner-edge shape ofthe diaphragm 101 c generally used, the relative position and anglerelations of the emitting generator 101 with respect to the detector 108are obtained. Consequently, without adding a special configuration thatspecifies the path of radiation, the position and angle of the emittinggenerator 101 at the time of image capturing can be grasped accurately.

The outer-edge shape of the radiation area irradiated with radiation onthe detection surface 108 s is recognized from the transmission images.Therefore, without adding a special configuration, the outer-edge shapeof the radiation area is recognized.

Using the information indicative of the accurately grasped position andangle of the emitting generator 101 in the image capturing, a sliceplane image is generated on the basis of a plurality of transmissionimages. Consequently, a high-quality slice plane image in whichoccurrence of so-called artifact is suppressed is obtained.

Second Preferred Embodiment

In the image capturing system 1 of the first preferred embodiment, theouter-edge shape of the radiation area is recognized from thetransmission images. On the other hand, in an image capturing system 1Aof a second preferred embodiment, an irradiation area on the detectionsurface 108 s is illuminated by lighting and is photographed by acamera. The outer-edge shape of the radiation area is recognized fromobtained photographed images.

The image capturing system 1A of the second preferred embodiment will bedescribed below. The image capturing system 1A of the second preferredembodiment has a configuration similar to that of the image capturingsystem 1 of the first preferred embodiment except for the configurationof recognizing the outer-edge shape of the radiation area. Consequently,the same reference numerals are designated to the similar components andtheir description will not be repeated. Mainly, the differentconfiguration will be described.

FIG. 13 is a diagram showing a schematic configuration of the imagecapturing system 1A according to the second preferred embodiment of thepresent invention.

The image capturing system 1A includes: an image capturing apparatus100A which has a emitting generator 101A to which an illuminatingmechanism 101 p (FIG. 14) is added in place of the emitting generator101 of the first preferred embodiment and a camera unit 106; and animage capture control processing apparatus 200A including a control unit210A having a functional configuration of recognizing the outer-edgeshape of the radiation area different from that of the control unit 210of the first preferred embodiment. A program PGA is stored in place ofthe program PG in the storing unit 240.

FIG. 14 is a cross section diagram schematically showing theconfiguration of the emitting generator 101A. The emitting generator101A is constructed by, for example, an X-ray tube and has thegenerating unit 101 a, the diaphragm 101 c, and the illuminatingmechanism 101 p. That is, the emitting generator 101A is obtained byadding the illuminating mechanism 101 p to the emitting generator 101 ofthe first preferred embodiment.

The illuminating mechanism 101 p is provided near the generating unit101 a and has a light source PR, a first reflection mirror M1, and asecond reflection mirror M2.

The light source PR has an apparatus for generating a visible light rayand generates, for example, a laser beam of a predetermined color. Thefirst reflection mirror M1 reflects the light from the light source PRtoward the second reflection mirror M2. The second reflection mirror M2reflects the light from the first reflection mirror M1, and light isemitted from the opening 101 h in the diaphragm 101 c to the detectionsurface 108 s. In FIG. 14, the path of light from the light source PR isshown by a thick broken-line arrow.

The path (optical path) of light generated by the light source PR andemitted via the diaphragm 101 c (concretely, the opening 101 h) is setalmost the same as the path (radiation path) of radiation emitted fromthe generator 101 a via the diaphragm 101 c (concretely, the opening 101h). That is, the illuminating mechanism 101 p is constructed so thatlight generated from the light source PR is applied to the detectionsurface 108 s via the optical path which is almost the same as theradiation path via the diaphragm 101 c.

In the second preferred embodiment, the mounting unit 104 is made of amaterial which transmits a visible light ray such as transparent glassso that the light is not blocked by the mounting unit 104. Further,since the second reflection mirror M2 is disposed on a path of radiationextending from the generating unit 101 a to the diaphragm 101 c(concretely, the opening 101 h), it is made of a material which easilytransmits radiation.

The camera unit 106 is a sensor constructed by, for example, a digitalcamera including an image capturing device such as a CCD, and is mountedjust above the mounting unit 104. Concretely, the optical axis of ataking lens of the camera unit 106 is almost orthogonal to the detectionsurface 108 s and passes almost the center of the detection surface 108s. That is, the camera unit 106 is mounted so as to face the detectionsurface 108 s.

More specifically, as shown in FIG. 13, the camera unit 106 is disposed,for example, in a position around the center in the extending directionof the guide 102 (for example, in FIG. 13, near the emitting generator101A drawn by the solid line) so as not to disturb the travel of theemitting generator 101A, the path of radiation emitted from the emittinggenerator 101A, and the optical path of light emitted from theilluminating mechanism 101 p.

The detection surface 108 s illuminated with the light from theilluminating mechanism 101 p is photographed from just above by thecamera unit 106 in the image capturing process using radiation, therebyobtaining an image. The image is transmitted to the control unit 210A.

FIG. 15 is a diagram paying attention to the emitting generator 101A,the detector 108, the specimen 120, and the camera unit 106 at the timeof imaging the specimen 120. As shown in FIG. 15, the position and theimage capturing direction of the camera unit 106 are fixed. The cameraunit 106 photographs the detection surface 108 s from a predeterminedposition irrespective of the position of the emitting generator 101A onthe guide 102.

The image obtained by the camera unit 106 has a pattern similar to thatof the transmission image G shown in FIG. 5 at the time of, for example,oblique imaging capturing as shown in FIG. 15. Specifically, the outeredges of the detection surface 108 s corresponding to the outer edges ofthe transmission image G and the area (illuminated area) illuminated bylight from the illuminating mechanism 101 p corresponding to the patternPA are captured.

The functional configuration of the control unit 210A will now bedescribed.

FIG. 16 is a diagram illustrating the functional configuration realizedwhen the program PGA is executed by the control unit 210A.

As shown in FIG. 16, the control unit 210A has, as functions, the imagecapturing control unit 211, the detection value obtaining unit 212, thevalue converting unit 213, a light-on control unit 214 a, a cameracontrol unit 214 b, a photographed-image obtaining unit 214 c, aradiation area recognizing unit 214 d, the position/angle computing unit215, and the image generating unit 216.

The image capturing control unit 211, the detection value obtaining unit212, the value converting unit 213, the position/angle computing unit215, and the image generating unit 216 are similar to those of the firstpreferred embodiment.

The light-on control unit 214 a controls light-on of the illuminatingmechanism 101 p, that is, emission of light from the light source PR.

The camera control unit 214 b controls the operation of the camera unit106. For example, light from the illuminating mechanism 101 p is emittedto the radiation area by the light-on control unit 214 a in accordancewith image capturing using radiation and the area is photographed by thecamera unit 106 to obtain a photographed image.

The photographed-image obtaining unit 214 c receives the photographedimage obtained by the camera unit 106. In the photographed-imageobtaining unit 214 c, a necessary image process may be performed.

The radiation area recognizing unit 214 d recognizes the outer-edgeshape of the radiation area irradiated with radiation on the detectionsurface 108 s emitted from the emitting generator 101A in a mannersimilar to the radiation area recognizing unit 214 of the firstpreferred embodiment except for a recognizing method.

The radiation area recognizing unit 214 d recognizes the outer-edgeshape of the radiation area in the photographed image obtained by thephotographed-image obtaining unit 214 c.

Specifically, the radiation area recognizing unit 214 d recognizes anarea irradiated with light in the detection surface 108 s by detecting,for example, a predetermined color or a high-illuminance part in thephotographed image obtained by the photographed-image obtaining unit 214c. The radiation area recognizing unit 214 d also recognizes the outeredges of the detection surface 108 s by, for example, edge detection.From the size of the detection surface 108 s and the size of the areairradiated with light, the length of the upper base, the length of thelower base, and the height of the trapezoid as the outer-edge shape ofthe radiation area are recognized.

In the position/angle computing unit 215 and the image generating unit216, processes similar to those of the first preferred embodiment areperformed by using the recognition results of the radiation arearecognizing unit 214 d.

FIG. 17 is a flowchart showing an image capturing operation flow ofcontinuously capturing transmission images of a plurality of frameswhile changing the radiation angle of X ray from the emitting generator101A to the specimen 120 in multiple stages in the image capturingsystem 1A. The operation flow is realized under control of, mainly, theimage capturing control unit 211 when the control unit 210A executes theprogram PGA. The operation flow starts when the specimen 120 is mountedon the mounting unit 104 and a predetermined input is entered from theoperating unit 230.

In steps SP1 to SP4, processes similar to those in steps S1 to S4 inFIG. 10 are performed.

In step SP5, under control of the light-on control unit 214 a,irradiation (illuminating) of the detection surface 108 s with light bythe illuminating mechanism 101 p starts.

In step SP6, under control of the camera control unit 214 b,photographing by the camera unit 106 is performed. A photographed imageof the detection surface 108 s irradiated with light is obtained by thephotographed-image obtaining unit 214 c.

In step SP7, under control of the light-on control unit 214 a, theirradiation (illuminating) of the detection surface 108 s with light bythe illuminating mechanism 101 p is finished.

In step SP8, the radiation area recognizing unit 214 d recognizes theouter-edge shape (concretely, the size) of the radiation area irradiatedwith radiation in the detection surface 108 s from the photographedimage obtained in step SP6.

In steps SP9 to SP11, processes similar to those of steps S6 to S8 inFIG. 10 are performed.

As described above, in the image capturing system 1A of the secondpreferred embodiment of the invention, in a manner similar to the imagecapturing system 1 of the first preferred embodiment, the relativeposition relation and the relative angle relation of the emittinggenerator 101A with respect to the detector 108 are obtained on thebasis of the outer-edge shape of the radiation area irradiated withradiation on the detection surface 108 s and the inner-edge shape of thepredetermined member (for example, the diaphragm 101 c) that specifiesthe path of radiation. Consequently, the position and angle of theemitting generator 101A at the time of image capturing can be graspedaccurately.

MODIFICATIONS

Although the embodiments of the present invention have been describedabove, the invention is not limited to the above description.

For example, in the foregoing embodiment, a slice plane image isgenerated by using the shift-and-add algorism. The invention is notlimited thereto. For example, while changing the radiation angle of Xray from the emitting generator 101 to the specimen 120 in multiplestages, a plurality of transmission images obtained are regarded as apart of transmission images obtained by the CT (Computed Tomography)image capturing technique. A slice plane image may be generated by usinga known filtered back projection method (FBPM) or the like as thetechnique of CT.

Although the inner-edge shape of a predetermined member (for example,the diaphragm 101 c) is a square and the outer-edge shape of theradiation area is a trapezoid or square in the foregoing embodiments,the invention is not limited thereto. When each of the inner-edge shapeof the predetermined member (for example, the diaphragm 101 c) and theouter-edge shape of the radiation area is a shape having four or morevertexes such as a rectangular or trapezoid, the distance “h” and theangle θ can be obtained by a computing method similar to that of theembodiment.

Although the distance “d” from the focal point Fp to the opening 101 his determined in designing in the foregoing embodiments, the inventionis not limited to the method. For example, when the distance “h” at theangle θ=0 is known, the distance “d” may be unconditionally calculatedfrom the size of the radiation area (for example, square) at that timeand the size of the inner-edge shape of the diaphragm 101 c.

In the second preferred embodiment, the detection surface 108 s isirradiated with visible light from the illuminating mechanism 101 p andphotographed by the camera unit 106, thereby obtaining a photographedimage. The invention however is not limited to the embodiment. It isalso possible to irradiate the detection surface 108 s with other lightsuch as infrared light and obtain a photographed image by using aninfrared camera or the like. To reduce an error in calculation in thedistance “h” an the angle θ, preferably, the linearity of light is highto some extent. For example, infrared light or light having a wavelengthshorter than that of the infrared light is desirable.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

1. A transmission image capturing system comprising: a generator forgenerating radiation; a predetermined member for specifying a radiationpath of said radiation by its inner-edge shape; a detector for detectingradiation emitted from said generator and passing through a specimen viasaid predetermined member; an obtaining unit for obtaining a pluralityof transmission images of said specimen by detecting the radiation for aplurality of times by said detector while changing a relative positionrelation and a relative angle relation of said generator to saiddetector; and a computing unit configured to obtain said relativeposition and angle relations on the basis of an outer-edge shape of aradiation area which is irradiated with the radiation emitted from saidgenerator to a detection surface of said detector and the inner-edgeshape of said predetermined member.
 2. The transmission image capturingsystem according to claim 1, wherein said predetermined member includesa diaphragm provided for said generator.
 3. The transmission imagecapturing system according to claim 1, wherein each of the outer-edgeshape of said radiation area and the inner-edge shape of saidpredetermined member has four or more vertexes.
 4. The transmissionimage capturing system according to claim 1, wherein the inner-edgeshape of said predetermined member includes a rectangular shape, and theouter-edge shape of said radiation area includes a trapezoid.
 5. Thetransmission image capturing system according to claim 1, furthercomprising a recognizing unit for recognizing the outer-edge shape ofeach of said radiation areas from said transmission images.
 6. Thetransmission image capturing system according to claim 1, comprising: alight beam irradiating unit for irradiating said detection surface witha light beam generated from a light source provided near said generatorvia said predetermined member along an optical path which is almost thesame as said radiation path; an image capturing unit for obtaining aphotographed image by photographing said detection surface irradiatedwith said light beam; and a recognizing unit for recognizing anouter-edge shape of said radiation area from said photographed image. 7.The transmission image capturing system according to claim 1, furthercomprising a generator for generating a slice plane image of saidspecimen on the basis of said plurality of transmission images by usingsaid relative position and angle relations obtained by said computingunit and corresponding to said transmission images.
 8. A transmissionimage capturing method of obtaining a plurality of transmission imagesby detecting radiation emitted from a generator and passing through aspecimen via a predetermined member for a plurality of times by adetector while changing a relative position relation and a relativeangle relation of said generator to said detector, comprising the stepsof: (a) recognizing an outer-edge shape of a radiation area irradiatedwith radiation on a detection surface of said detector from saidgenerator; and (b) obtaining said relative position and angle relationson the basis of the outer-edge shape of said radiation area and theinner-edge shape of said predetermined member.